Method of using intrinsically conductive polymers with inherent lubricating properties, and a composition having an intrinsically conductive polymer, for protecting metal surfaces from galling and corrosion

ABSTRACT

A method for protecting a metal surface from galling and corrosion includes a step of providing a protective dry film on the metal surface. The film includes a solid lubricant and a conducting polymer, the conducting polymer having lubricant properties and being capable of binding the solid lubricant to the metal surface. Threaded metal joint surfaces coated with the film are capable of resisting galling under high pressure and high torque conditions, even after several fastening and unfastening operations or over a long period of time. Protection from corrosion is also provided by the film. The method and film are economical in that only a single layer of protective compound need be applied in order to provide metal surfaces with both lubrication and protection against corrosion, and problems such as removal or leakage, which are associated with protective compounds that use oils, are avoided. Additionally, the dry film is advantageous because it does not contain heavy metals that are harmful to the environment.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to corrosion-protection and lubrication of metalsurfaces. In particular, the invention relates to a method of protectinga metal surface, such as the surface of threaded joints in oil tubingsor casings, by applying a dry film including a binding intrinsicallyconductive polymer to the surface. The invention also relates to acomposition for protecting a metal surface from galling and corrosion.

2. Description of the Related Art and Problem to be Solved

A. Intrinsically Conductive Polymers and Corrosion Protection

Intrinsically conductive polymers used as corrosion protection compoundsare known in the art. One example of an intrinsically conductive polymeris polyaniline, which has been known to modify the electrochemical andcorrosion behavior of stainless steels. For example, DeBerry hasdetermined that stainless steel electrodes coated with thin films ofpolyaniline remain passive for long periods of time in acid solutions,even though normally they would be active and highly susceptible tocorrosion in such environments (J. Electrochem. Soc.: ElectrochemicalScience and Technology 132 (5) (1985) 1022-1026). According to Gasparacet al., who have examined the mechanism of corrosion inhibitionconferred by polyaniline on steel placed in a highly corrosive sulfuricacid solution, passivation is achieved because the polyaniline holds thepotential of stainless steel electrodes in a passive region, preventingcorrosion (J. Electrochem. Soc. 148 (4) (2001) B138-B145).

Polyaniline can be an electrical conductor depending on its state ofoxidation or doping. The corrosion protection mechanism involves boththe conductive and the non-conductive states of polyaniline.

Wessling et al. (Synth. Met. 85 (1997) 1313-1318) have proposed acorrosion protection mechanism including the following steps: 1)Polyaniline in its conductive state (i.e., emeraldine base) depolarizesferrous metal by accepting electrons, forming non-conductive polyaniline(leucoemeraldine). 2) Atmospheric oxygen regenerates the polyaniline toits conductive state (emeraldine).

Further, Gasparac et al. (J. Electrochem. Soc. 148 (4) (2001) B138-B145)have confirmed the proposed mechanism using polyaniline on stainlesssteel in the presence of oxygen.

Lu et al. have disclosed corrosion protection of mild steel by coatingscontaining polyaniline (Synth. Met. 71 (1995) 2163-2166), while Camaletet al. have disclosed the electrodeposition of protective polyanilinefilms on mild steel (J. Electroanalytical Chem. 416 (1996) 179-182).Rajagopalan et al. have disclosed two-intrinsically conductive-polymer,polyaniline-polypyrrole composite coatings formed on low carbon steelusing an aqueous electrochemical process, which have anti-corrosiveproperties (Surface Engineering 18 (1) (2002) 53-63). And Kraljic et al.have disclosed inhibition of steel corrosion by polyaniline coatingselectrosynthesized on steel samples using sulfuric and phosphoric acidsas supporting electrolytes (Corrosion Science 45 (2003) 181-198).

Previously, intrinsically conductive polymers have been provided onmetal surfaces through direct application by electropolymerization ontoa metal surface, as well as by deposition of solutions of previouslypolymerized monomers.

In methods involving the deposition of a solution of previouslypolymerized monomers, the polymer has been included in a binding, suchas a polyaliphatic-diamine resin (U.S. Pat. No. 6,500,544 to Tiitu etal.), or an acrylate (European Patent Application No. 1 258 513 A2, Rohmand Haas Company).

Intrinsically conductive polymers have also been used as general bindingagents and combined in composites with corrosion protection agents, suchas 2,5-dimercapto-1,3,4 thiadiazole or trithiocyanuric acid (U.S. PatentPublication 2002/0197468 A1, Sinko).

The term “inherently conductive” or “intrinsically conductive” issometimes used (for example, in U.S. Pat. No. 5,567,355 to Wessling etal.) to describe conjugated materials (such as polyaniline) that do notrequire the addition of conductive materials (such as carbon or metalparticles), but may or may not require doping (oxidation and/orprotonation), in order to be conductive. Inherently conductive orintrinsically conductive polymers can thus be distinguished from“common” polymers (such as poly[methyl methacrylate]), which require aconductive material (such as graphite) dispersed therein to give thepolymer conductivity.

Unlike non-conductive polymers such as titanates, silicones, epoxies,polyurethanes, and the like, the conductive properties of polyanilineaccount for both the anticorrosion mechanism and the possibility of anindustrial application by electrodeposition or electrophoresis in asingle step at high speed, without the use of solvent, thus reducingslow drying steps. Polyaniline can also be sprayed or brush-painted onmetal surfaces, like other polymers.

B. Lubricants and Galling Protection

Galling is a form of surface damage arising between sliding solids,distinguished by macroscopic, usually localized, roughening and creationof protrusions above the original surface. It often includes plasticflow or material transfer, or both. (ASTM definition.) A number ofsurface treatments are known for protection from galling of metalsurfaces, such as the threaded connections of oil pipe joints.

For instance, molybdenum disulfide, colloidal graphite, and othercompounds that present similar lamellar structures in the solid phaseare commonly used as lubricants of metal surfaces. Such solid lubricantshave been included in dry films with ketonic resins (U.S. Pat. No.4,692,988 to Shulver), epoxy resins (Chinese Patent No. 1218100 toLanzhou Chem. Phys. Institute), and specially fluorinatedpoly[alkylidenes] (U.S. Pat. No. 5,407,590 to Salvia) or polyethers(U.S. Pat. No. 4,692,988 to Shulver) as binders and applied onto metalsurfaces by different methods. Since the resins will usually cure onceapplied onto a metal surface, compositions usually include a curingagent and may contain toughening agents in the case of rubber binders.

However, the art does not disclose a method of using intrinsicallyconductive polymers with inherent lubricating properties, and a dry filmhaving an intrinsically conductive polymer, for protecting metalsurfaces from galling and corrosion.

For example, U.S. Pat. No. 4,414,247 to Hubecker proposes a method ofsurface treatment of threading that involves the use of a resin varnishwith a dispersion of particles of solid molybdenum disulfide lubricant.However, no corrosion protection is provided.

U.S. Pat. No. 4,692,988 to Shulver proposes applying a dry lubricantsuch as molybdenum disulfide to a screw thread, and applying a liquidlubricant such as oil to the other screw thread, during the assembly ofa connection. Therefore, the patent does not disclose a dry lubricatingprocess. It also does not disclose the use of conductive polymer tolubricate or protect from corrosion.

PCT Publication WO 02/18522 A1 (Vallourec Mannesmann Oil & Gas France,and Condat S. A.), which relates to a threaded joint for oil well pipes,also teaches the use of oil in a lubricating substance applied to athreaded component, so it cannot be considered to disclose a drylubricating process.

PCT Publication WO 01/16516 A1 (Sumitomo Metal Industries, Ltd.)discloses a rust-inhibiting coating including a layer of oil containingrust inhibitors. This coating is applied to a threaded joint, over acoating of dry lubricant, and must be removed in the oil field beforeassembling the connection, thus complicating operations.

U.S. Pat. No. 6,027,145 to Tsuru et al., which relates to a threadedjoint having high galling resistance, discloses a resin coating layer inwhich at least one powder selected from the group consisting ofmolybdenum disulfide and tungsten disulfide is dispersed and mixed. Theresins are epoxy, furan, or polyamide, which are very different from theconductive polymers of this invention. The resin layer is formed on, andhas a thickness larger than, a phosphate chemical formation coatinglayer. The patent does not teach the use of an intrinsically conductivepolymer layer as an anti-galling and anti-corrosive coating, alone or incombination with molybdenum disulfide.

U.S. Patent Publication 2002/0166770 A1 (Kimpel et al.) discloses aprocess for producing a multi-layer coating. A primer layer, which iselectrically conductive in the at least partially-cured state, isapplied by electrodeposition from an electrodeposition coating agent (I)to an electrically conductive object. The primer layer is at leastpartially cured exclusively by the action of near infra-red radiation,and an additional coating layer is applied by electrodeposition from anelectrodeposition coating agent (II). The additional coating layer, aswell as completely uncured or incompletely cured area parts of theprimer layer, are then cured. The electrodeposition coating agent (I)contains one or more electrically conductive constituents, which confera volume resistivity on the electrodeposition coating layer and mayinclude, among other possibilities, graphite, molybdenum disulfide, orintrinsically conductive polymers such as polyaniline. This publicationdoes not teach that the multi-layer coating has lubricant properties.

U.S. Patent Publication 2002/0114940 (Clemens et al.) discloses acoating system that includes a basecoat of a thermosetting asphaltextended, chemically cross-linked urethane/epoxy hybrid basecoat restingon a substrate, and a thermoplastic powder coating topcoat overlying atleast the base coat. Corrosion inhibitors, which include polyaniline,and fillers and lubricants, which include molybdenum disulfide, areoptionally included in the coating system. According to thispublication, polyaniline is used as a corrosion protection additive, notas a binding intrinsically conductive polymer.

Italian Patent Application RM 2002 A000512 (Tenaris Connections Ltd./AG)discloses a surface treatment including a first uniform layer of a drycorrosion inhibiting coating and a second uniform layer of a drylubricant coating applied over the first layer. It also discloses auniform layer of dry corrosion inhibiting coating that contains adispersion of particles of solid lubricant. However, the applicationdoes not teach a homogeneous layer of an intrinsically conductive,anti-corrosive polymer, which itself prevents galling and may be mixedwith solid lubricant particles.

U.S. Pat. No. 5,980,723 to Runge-Marchese et al. discloses ananodization process for forming a composite polymer-metal oxide film ona metallic substrate, such as aluminum. The process includes the stepsof anodizing the metallic substrate, thereby forming an anodic film, andsimultaneously depositing a polymer within the anodic film. Theanodizing and depositing steps employ an electrolyte including anintrinsically conductive polymer, such as sulfonated polyaniline, and aprotonic acid solution as an oxidizing agent. According to the patent,metal oxide formation is required. The composite polymer-metal oxidefilm can be formed on other metal substrates aside from aluminum, suchas copper, steel, silicon, zinc, magnesium, or titanium. However, sinceanodization cannot be performed on iron (and iron-based alloys) orcarbon steel surfaces, iron and carbon steel are not suitable metalsubstrates for the process of Runge-Marchese et al.

None of the above documents discloses a dry coating that is based on adispersion of a solid lubricant in an inherently or intrinsicallyconductive polymer that is both an anticorrosive and a lubricant initself.

Although polyaniline by itself is a lubricant that shows goodanti-galling properties and also protects from corrosion, it actssynergistically with molybdenum disulfide in terms of anti-gallingprotection. Accordingly, in one embodiment according to our invention,described more fully later, polyaniline is combined with molybdenumdisulfide in a surface composite.

SUMMARY OF THE INVENTION

It is an object of the invention to provide protection from galling tometal surfaces, particularly threaded joint surfaces in oil tubing andcasing subjected to high pressure, high friction, and high torqueconditions.

It is another object of the invention to provide both galling-protectionand corrosion-protection to metal surfaces through a simple applicationof a single compound.

The invention makes use of intrinsically conductive polymers, previouslydescribed as a corrosion protection agent, as non-oily and non-liquidorganic lubricants for metal surfaces.

In one aspect according to the invention, a method for protecting ametal surface from galling and corrosion is provided. The methodincludes a step of applying a dry film comprising a bindingintrinsically conductive polymer to the metal surface. The intrinsicallyconductive polymer itself has lubricant properties and is capable ofbinding solid lubricants to the metal surface.

The invention provides, in another aspect, a composition for protectinga metal surface from galling and corrosion. The composition includes abinding intrinsically conductive polymer with lubricant properties, anda solid lubricant.

In an embodiment of the invention, a surface treatment comprises thedeposition onto a metal surface of a dry film including polyaniline, thepolyaniline having lubricating properties and acting as a binding agentfor molybdenum disulfide. The dry film may contain high amounts of themolybdenum disulfide, for example, in a proportion of four times thepolyaniline by mass. The surface treatment may include pretreatment ofthe metal surface through chemical deposition of a conversion coating(that is, a coating that chemically changes the surface of a metallicpart) such as, for example, manganese phosphate, zinc phosphate,oxalate, and the like; or chemical deposition of a copper layer ontohigh chromium alloy.

Surface protection is achieved by mechanical deposition onto the metalsurface of mixtures of the molybdenum disulfide and the polyanilinedissolved in an adequate solvent. Suitable methods of mechanicaldeposition include painting with a brush or spraying by aerosol. Surfaceprotection may also be achieved by electropolymerization onto the metalsurface of the anilines/monomers in the presence of the molybdenumdisulfide and other additives. Electrodeposition can be obtained byapplying a suitable (electrode) potential to the metal surface immersedin an electrolytic aqueous solution containing aniline/monomer.Alternatively, the molybdenum disulfide can be entrapped in apolyaniline/polymer film by electrophoretic deposition of thelubricating mixture onto the metal surface.

Additives may be included in the dry film in order to enhance propertiessuch as anti-corrosive properties, high stability of thepolyaniline-molybdenum disulfide mixture, or improved adherence of thedry film. The properties of the dry film can also be modified bypost-chemical treatment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of the set-up of a ring-on-disk test.

FIG. 2 shows an enlarged cross-section of part of the set-up of FIG. 1.

FIG. 3 is a graph of a typical result of a ring-on-disk test

FIG. 4 is an SEM image of a sliding surface, showing severe gallingafter a ring-on-disk test.

FIG. 5 is an SEM image, taken after a ring-on-disk test, of the slidingsurface of a phosphated disk treated with dry film (polyaniline+MoS₂).

FIG. 6 is an SEM image, taken after a ring-on-disk test, showing detailof the sliding surface of a phosphated disk treated with dry film(polyaniline+MoS₂).

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to composition, preparation, andapplication of a dry film to steel and other metal surfaces, such as thesurface of a threaded joint in an oil pipe, in order to protect themetal against galling under high applied torque, as well as to conferresistance to corrosion.

The dry film of the invention comprises a solid lubricant selected fromthose commonly used for lubrication purposes, such as molybdenumdisulfide, graphite, or mixtures thereof; and a binding intrinsicallyconductive polymer such as polyaniline, polyprrole, or copolymers ormodifications of these polymers.

Polyaniline used in the dry film may be prepared according to variousmethods, such as those described by Ponzio et al. (Polym. Int 50 (2001)1180-1185), Cao et al. (Polymer 30 (1989) 2305-2311), Stejskal et al.(Synth. Met. 105 (1999) 195-202), Sun et al. (Synth. Met. 84 (1997)99-100), Mattoso et al. (Synth. Met. 68 (1994)1-11), Singh et al.(Polymer 38 (1997) 4897-4902), U.S. Pat. No. 5,519,111 to McDiarmid etal., and U.S. Pat. No. 5,567,355 to Wessling et al. A survey of methodsof synthesis of polyaniline and its properties is reported by Genies etal. in Synth. Met. 36 (1990) 139-182, and a standardized test protocolfor preparation of polyaniline is reported by Stejskal et al. in PureAppl. Chem. 74 (5) (2002) 857-867.

Modified polyaniline can also be used for preparation of the dry film.Modification may be carried out on the polymer, both in the ring (Yue etal., J. Am Chem. Soc. 113 (1991) 2665-2671) and in the nitrogen (Hwanget al. Synth. Met. 92 (1998) 39-46). Further, it is possible topolymerize a chemically-modified monomer or a mixture of monomers toobtain copolymers (see, for example, Mattoso et al., Synth. Met. 68(1994) 1-11).

The presence of a solid lubricant is not necessary in the dry film. Byitself, a conducting polymer, such as polyaniline, has lubricating oranti-galling properties as well as anti-corrosion properties. Forinstance, a simple polyaniline prepared and applied onto a metal surfacein a manner according to the invention provides a lubricating coatingthat performs comparably or even better than many conventional oils.Further, the dry film does not pose the leakage problems associated withconventional oils. Nor does it contain heavy metals (such as lead),which oils often have, that are harmful to the environment.

Nevertheless, performance of the dry film used in the invention isimproved when the film includes a high concentration of solid lubricant.As an example, addition of molybdenum disulfide in a 4:1disulfide-to-polymer weight ratio improves the lubrication between twometal surfaces under pressure.

Preferably, the dry film has polyaniline in its emeraldine base form asthe intrinsically conductive polymer, and molybdenum disulfide as thesolid lubricant, in a 1:4 to 1:2 weight ratio. The best performance canbe achieved by dissolving these components in fifty parts by weight ofN-methylpyrrolidone (NMP) solvent. This liquid composite is then sprayedover a cleaned metal surface to be treated. Once the metal surface isdry, another layer of liquid composite may be applied, and best resultsare obtained by applying about 5 to 20 twenty layers of the composite byrepeating the process described. The typical thickness of the drysupported lubricant film is about 1 to about 2 micrometers per layer ofapplied liquid composite, depending on the concentration ofintrinsically conductive polymer in the liquid composite.

According to the invention, the dry film does not require additives tohelp achieve protection against galling and corrosion. However, suchadditives, like dispersing agents for the solid lubricants or agents forstabilizing highly concentrated polymer solutions, are not excluded.Other agents may be a complementary inhibitor added to improve corrosionresistance, and a surfactant added to stabilize a suspension of thesolid lubricant. In cases in which the dry film is provided byelectrodeposition, possible additives may also include, for example, anagent for improving compatibility of a monomer and a solid lubricant ina particular solvent.

The dry film may be applied to metal surfaces by any physical method fordeposition of a liquid composite, such as application by spray or bypainting with a brush. The film may also be applied by electrophoresis,as well as electropolymerization of monomers (or mixtures of monomers)in the presence of a solid lubricant or mixtures of solid lubricants.Preferably, the liquid composite is applied by spray, which has anadvantage of producing more homogeneous films and lends itself to use infield application and inclusion in a repair kit.

The dry film may be applied onto a bare metal surface such as iron,steel, or stainless steel. It can also be applied, for example, onto acopper layer or a manganese phosphate layer previously deposited onto ametal surface. When one of the surfaces involved in a joint or in afriction couple (“pin and box” in the oil industry) is chemicallypretreated by manganese phosphate, higher galling resistance has beenobserved. In the case in which the dry film is provided byelectrodeposition, manganese phosphate and the conducting polymer layermay be co-deposited, or simultaneously grown.

In one preferred embodiment of the invention, the dry film is applied tothe surface of a box (that is, the internal female threaded end of aconnection) pre-treated with manganese phosphate. The corresponding pin(that is, the external male threaded end of a connection) is coated withpolyaniline only, to provide additional corrosion protection to thepin-and-box couple.

The method and dry film of the invention are further illustrated in thefollowing non-limiting examples.

Preparation of the Liquid Composite

Polyaniline (or polypyrrole) is first prepared by chemicalpolymerization of aniline (or pyrrole) with sodium persulfate as anoxidant in the presence of sulfuric or phosphoric acid.

When the polymerization reaction is complete, the polyaniline, whichwill be in its emeraldine oxidation form (protonated or salt form), isfiltered. The green powder is then re-suspended in a stirred solution ofammonium hydroxide for a few hours, after which the solution is filteredagain and the dark blue polymer (emeraldine base form) is dried until nowater remains. High reaction yields, of over about 70%, are obtained.

If the polymer is not used immediately, care must be taken to keep itdry. Alternatively, it should be re-dried prior to preparation of itsliquid solution for application to metal surfaces. Drying conditions aretypically 3 hours at 60° C. or overnight in a vacuum oven at 40° C.

Then, with intense stirring, dry polyaniline is slowly dissolved in NMPin a preferred range of about 2% to about 5% by weight. After additionof all of the polymer, the solution is left to stand for a few minutes,though no more than about 10 minutes in order to avoid formation ofgels. Solutions prepared in the above manner remain stable for at leastseveral weeks.

Solid lubricant may be added to the polymer solution with continuousstirring during the addition. Preferably, the mass of lubricant isadjusted so that it is in about a 1:4 ratio by weight in relation to thepolymer, or about 2% to about 10% by weight in relation to the solvent.

Anti-Galling Tests

The dry film was tested on 1% Cr steel surfaces in two experiments, ineach of which a metal joint was subject to high friction conditions inorder to test resistance to galling or delay in the appearance ofgalling.

FIGS. 1 and 2 depict schematics of a “ring-on-disk” test layout.Reference numeral 10 denotes an electric motor that applies rotation toa ring-shaped part (24 in FIG. 2) at a given speed. Reference numeral 20corresponds to a ring-and-disk sample set being evaluated: the samplecomprises the ring-shaped part 24 (FIG. 2) and a disc-shaped lower part(26 in FIG. 2). Reference numeral 30 denotes a torque load cell which isa device used to measure the resultant torque; reference numeral 40denotes an axial load cell that measures applied axial load; andreference numeral 50 denotes a hydraulic piston employed to apply acontrolled axial load (22 in FIG. 2 denotes an axis of loadapplication).

In the first test, a ring-on-disk experiment, two plane surfaces werepressed together, and the upper surface was rotated under an appliedpressure while the lower surface remained fixed. The upper plane surfacecorresponds to the base of the ring-shaped part 24 that usually is notchemically treated, and the disc-shaped lower piece 26 is eitherpretreated by chemical deposition of manganese phosphate, glass peening,or sanding, or not pretreated at all.

The dried film can be applied by either physical deposition of theliquid composite or by electrochemical or electrophoretic techniques.

The ring-on-disk test consisted of monitoring torque over time. FIG. 3is a graph of a typical test result. The applied pressure between ringand disk was increased up to 30 Kg/mM² and after that was kept constant.The torque value increased with the applied pressure. When the maximumpressure was reached, the torque value decreased and then remainedalmost constant, indicating a good lubrication process. When gallingoccurred, sharp fluctuations in torque value were observed. The timethat elapses until the fluctuations begin is considered thecharacteristic time for the test.

FIG. 4 is a scanning electron micrograph (SEM) image of a slidingsurface, not treated with the dry film, showing severe galling after aring-on-disk test. FIGS. 5 and 6 are SEM images, taken after aring-on-disk test, of the sliding surface of a phosphated disk treatedwith dry film (polyaniline+MoS₂). No galling was observed even afterseveral hours of testing.

Table 1 shows that direct application over steel surfaces pretreatedwith manganese phosphate results in similar or better performance thanapplying commonly-used oily liquid lubricants. TABLE 1 Ring-on-disk testresults Coating applied to phosphated Average time steel disk beforegalling occurs No lubricant applied 44 seconds Metal-free industrialthread compound 480 seconds Industrial thread compound containing 650seconds copper and zinc API thread compound containing 959 to 1469seconds copper, zinc, and lead Polyaniline + MoS₂ composite >10,000seconds (1:2 and 1:4 weight ratios)

In the second experiment, couplings and pins of several diameters, ofthe type commercially known as “premium connection,” were covered withthe dry film and subjected to full scale “make-up and break-out” (M&B,thread-fastening and unfastening) operations conducted in accordancewith ISO 13679 petroleum and natural gas industry procedures for thetesting of casing and tubing connections. The dry film of the inventionprovided excellent lubrication and galling resistance to the connectionseven after the number of make-up and break-out cycles required by theISO Standard had been exceeded. In Table 2, some typical full scale M&Btest results for connections of different diameters and steel grades arepresented. TABLE 2 Full scale M&B test results Pin Diam. Steel Treat-Coupling N^(o) M&B [in] Grade ment Treatment M&B Galling Required 3 ½T95 Dry MnPO₄ 21 Yes 9 Film 3 ½ T95 Dry MnPO₄ 16 Yes 9 Film 2 ⅞ P110Bare MnPO₄ + 28 NO 9 Dry Film 4 ½ P110 Bare MnPO₄ + 19 Yes 9 Dry Film 4½ P110 Bare Dry Film 19 Yes 9 4 ½ P110 Bare Dry Film 18 Yes 9 7 L80 BareMnPO₄ + 12 Yes 9 Dry Film 9 ⅝ L80 Bare MnPO₄ + 20 NO 2 Dry Film 9 ⅝ L80Bare MnPO₄ + 20 NO 2 Dry Film 9 ⅝ L80 Bare MnPO₄ + 10 NO 2 Dry Film 9 ⅝L80 Bare MnPO₄ + 10 NO 2 Dry Film 9 ⅝ L80 Bare MnPO₄ + 10 NO 2 Dry Film9 ⅝ L80 Bare MnPO₄ + 10 NO 2 Dry Film* Dry Film: polyaniline + MoS₂ composite* N^(o) M&B: number of make-up and break-out cycles.a) Where the entry in the Galling column is “Yes”, the N^(o) M&B numberindicates the cycle during which galling took place.b) Where the entry in the Galling column is “NO”, the N^(o) M&B numberindicates the number of cycles that elapsed, with no evidence ofgalling, before testing was stopped.* Entries in the M&B Required column refer to the number of make-up andbreak-out cycles without galling required by the ISO 13679 standard.

Anti-Corrosion Test

Phosphated (manganese) 1% Cr steel samples and couplings were sprayedwith the liquid composite, providing a dry composite layer with athickness of between 2 and 20 microns. The samples were tested in a saltspray (fog) chamber following the ASTM B 117 Standard Practice forOperating Salt Spray (Fog) Apparatus. Only after 600 hours of testingwas corrosion observed on the samples, indicating good corrosionprotection. Also, in testing of couplings exposed to a humid environment(riverside), no corrosion occurred even after three months of exposure.

While particular embodiments of the invention have been illustrated anddescribed, it will be apparent to those skilled in the art that variouschanges and modifications may be made without departing from the spiritand scope of the invention. Furthermore, it is intended that the claimswill cover all such modifications that are within the scope of theinvention.

INDUSTRIAL APPLICABILITY

This invention provides a method for protecting a metal surface fromgalling and corrosion, and a composition for protecting a metal surfacefrom galling and corrosion. We envision that the method and thecomposition can preferably be applied, for example, to any type of metalthread and any type of metal oil-pipe joint commonly used in the oilindustry, in order to confer resistance to galling and corrosion in asimple and economical manner.

1. A method for protecting a metal surface from galling and corrosion,said method comprising the step of: providing a dry film on the metalsurface, the dry film comprising a binding intrinsically conductivepolymer; wherein the intrinsically conductive polymer itself haslubricant properties and is capable of binding solid lubricants to themetal surface.
 2. The method according to claim 1, wherein the dry filmincludes a solid lubricant.
 3. The method according to claim 1, whereinthe dry film is formed by application to the metal surface of a liquidsolution of the intrinsically conductive polymer.
 4. The methodaccording to claim 2, wherein the dry film is formed by application tothe metal surface of a liquid composite comprising the intrinsicallyconductive polymer and the solid lubricant in a solvent.
 5. The methodaccording to claim 4, wherein the dry film is formed by drying a wetfilm of the liquid composite which has been applied on the metal surfacewith a brush.
 6. The method according to claim 4, wherein the dry filmis formed by drying the liquid composite which has been applied on themetal surface by spraying.
 7. The method according to claim 1, whereinthe dry film is formed by electropolymerization.
 8. The method accordingto claim 1, wherein the dry film is formed by electrophoretic depositionof the intrinsically conductive polymer.
 9. The method according toclaim 1, wherein the dry film is formed by electrophoretic deposition ofthe intrinsically conductive polymer in the presence of at least onesolid lubricant.
 10. The method according to claim 1, wherein theintrinsically conductive polymer is polyaniline, in a concentration in arange of about 1% to about 20% by weight of the dry film.
 11. The methodaccording to claim 1, wherein the intrinsically conductive polymer is aring-substituted polyaniline, a nitrogen-substituted polyaniline, or apolyaniline copolymer in a concentration in a range of about 1% to about20% by weight of the dry film.
 12. The method according to claim 2,wherein the solid lubricant is molybdenum disulfide.
 13. The methodaccording to claim 2, wherein the solid lubricant is graphite.
 14. Themethod according to claim 12, wherein the intrinsically conductivepolymer is polyaniline in its emeraldine base form, in apolyaniline-to-molybdenum disulfide weight ratio of about 1:4 to about1:2.
 15. The method according to claim 14, wherein the emeraldine andthe molybdenum disulfide are dissolved in fifty parts by weight ofN-methylpyrrolidone solvent.
 16. The method according to claim 4,wherein plural layers of the liquid composite are successively applied,a first layer being applied directly to the metal surface to form thedry film, and each successive layer being applied over a previous layerwhen the previous layer has dried.
 17. The method according to claim 16,wherein about 5 to about 20 twenty layers of the liquid composite aresuccessively applied.
 18. The method according to claim 16, wherein thethickness of each of the layers is about 1 to about 2 micrometers. 19.The method according to claim 1, wherein a conversion coating isprovided on the metal surface before said step of providing the dryfilm.
 20. The method according to claim 19, wherein the conversioncoating is selected from the group consisting of manganese phosphate,zinc phosphate, and oxalate.
 21. The method according to claim 1,wherein a conversion coating and the conducting polymer are co-depositedon the metal surface.
 22. The method according to claim 21, wherein theconversion coating is selected from the group consisting of manganesephosphate, zinc phosphate, and oxalate.
 23. A composition for protectinga metal surface from galling and corrosion, said composition comprising:a binding intrinsically conductive polymer with lubricant properties;and a solid lubricant.
 24. The composition according to claim 23,wherein said intrinsically conductive polymer is polyaniline or achemical modification of polyaniline in any of its oxidation states, ina concentration in a range of about 1% to about 20% by weight of saidcomposition.
 25. The composition according to claim 23, wherein saidintrinsically conductive polymer is sulfonated polyaniline having anydegree of sulfonation, in a concentration in a range of about 1% toabout 20% by weight of said composition.
 26. The composition accordingto claim 23, wherein said solid lubricant is molybdenum disulfide. 27.The composition according to claim 23, wherein said solid lubricant isgraphite.
 28. The composition according to claim 26, wherein saidintrinsically conductive polymer is polyaniline in its emeraldine baseform, in a polyaniline-to-molybdenum disulfide weight ratio of about 1:4to about 1:2.
 29. The composition according to claim 28, wherein theemeraldine and the molybdenum disulfide are dissolved in fifty parts byweight of N-methylpyrrolidone solvent.
 30. An improved metal threadedconnection that is resistant to corrosion and galling, comprising: aphosphatized female threaded part having a first surface provided with adry film comprising intrinsically conductive polyaniline and molybdenumdisulfide; and a male threaded part having a second surface to be incontact with the first surface, the second surface being provided with adry film comprising intrinsically conductive polyaniline.